User:Audreyf123/Renal tissue kallikrein

The EC number is numerical nomenclature used for classifying enzymes. Tissue kallikrein having EC 3.4.21.35, indicates hydrolases, peptidases, serine endopeptidases, and tissue kallikrein respectively. [1]

Enzyme’s reaction pathway

As the largest group of serine proteases, tissue kallikreins are located on human chromosome 19q13.4. This consists of 15 genes and a pseudogene. These genes are referred to as KLK. Steroid hormones are what regulates this gene expression. The mRNA that encodes its genes are translated to an inactive form, which are either auto-activated or activated by proteases. KLKs can also be regulated by inhibitors or ions (such as zinc). [2]

Tissue kallikrein is regulated by (lysyl-bradykinin (Lys-BK or kallidin) and bradykinin (BK). Kininases I and II and endopeptidase degrade kinins to produce kinin metabolites. Kinins are able to bind to bradykinin B2 receptors, which are continually expressed, and kinin metabolites to bradykinin B1 receptors, which are present in the presence of trauma. The kinins binding activates a cascade signaling pathway in the cell (NO–cGMP, prostacyclin–cAMP, ect.) resulting in larger effects such as vasodilation, smooth muscle contraction and relaxation, inflammation and pain. These pathways can be blocked by icatibant, Des-Arg9-[Leu8]-BK, and kallistatin. The kallikrein–kinin system is linked with renin–angiotensin system (RAS) by the enzyme angiotensin-converting enzyme (ACE). [2][3]

Kallikrein sequences have been found in homo sapiens (human), Mus musculus (mouse), Bos taurus (cattle), Canis familiaris (dog), Monodelpis domestica (opossum), Procavia capensis (hyrax), Macropus eugenii (wallaby), Xenopus tropicalis (frog), Ornithorhynchus anatinus (platypus), Anolis carolinensis (lizard), Meleagris gallopavo (turkey), Taeniopygia guttata (Zebra Finch), and Gallus gallus (chicken). [4]

How this enzyme functions in the cell (tie reaction to larger metabolism)

Kallikreins are synthesized into the cell’s extracellular space in their inactive form. They are then activated by the trypsin cleavage at the Lys21-Leu22 peptide bond either autocatalytically or other endogenous proteases. This allows the N-terminal region to fold in the direction of the proteins surface leading to conformational rearrangements and the formation of salt bridges. In addition surface loops are also rearranged. [5]

With the expression of KLKs, and its regulation by steroid hormones, many biological functions can result such as roles in tissue remodeling, prohormone processing, neural plasticity, cancer-related processes such as cell growth regulation, angiogenesis, invasion, and metastasis. Specific KLKs can contribute to tooth development, skin desquamation, reproduction, remodeling and tumor invasion, and even neural plasticity. [4]

Structure

Kallikrein structures have a typical chymotrypsin fold containing two domains, six beta barrels and three loops between domains. These structures have ten conserved cysteine residues forming five disulfide bridges for stability. However, there is slight variation between different KLKs. [5]

Description of known active sites

The active sites contain three amino acids, His57, Asp102, Ser195, found in the interface of the domains. The presence of either Asp189 or Ser189 in the S1 active site determines the cleavage specificity and preference based on basic or hydrophobic amino acids. [5]

Problems present in the regulation of KLK activity are associated with including respiratory diseases, neurodegeneration, anxiety, schizophrenia, skin-barrier dysfunction, pathological inflammation, and cancer. As mentioned above the S1 substrate-binding site determines the substrate specificity. [5]

The genes encoding tissue kallikrein either synthesize trypsin-like (KLK1, KLK2, KLK4, KLK5, KLK6, KLK8, KLK10, KLK11, KLK12, KLK13, KLK14, KLK15) or chymotrypsin-like (KLK3, KLK7, KLK9) variations. Demonstrating the large variability and specificity of this enzyme's function. [6]